1. Field of the Invention
The present invention relates to a developing apparatus in an image forming apparatus using electrophotographic method such as a copying machine, printer, facsimile machine, or combined machine of them, specifically to a developing apparatus in an image forming apparatus, having a transfer means for transferring developer to a developing roller for developing the latent image on a photo conductor while agitating the developer and a toner accommodating means such as a toner container from which the toner is supplied to a toner agitation/transfer means.
2. Description of the Related Art
Among electrophotographic image forming apparat uses, there is one in which a developing roller carrying the developer containing toner for developing a latent image formed on a photo conductor and an agitation/transfer means of developer for supplying charged toner to said developing roller are used. There has been proposed a developing apparatus, for example, in which a sensor for detecting toner concentration and a toner container detachably mountable to said main assembly of a developing apparatus detachable from the developing apparatus are provided, the toner in the container being able to be supplied by a signal from a control circuit, and the toner is supplied from the toner container when the toner concentration in the developer decreases with decreased amount of the toner as the toner is consumed for developing the latent image on the photo conductor.
There is also proposed a developing apparatus with which toner is supplied not only when toner concentration has decreased, as disclosed in Japanese Patent Laid-Open Publication No. 2002-72645, in which a mechanism for reciprocating a toner cartridge to supply toner is provided to move the toner toward a discharge opening formed in an end in the toner cartridge, and the toner is allowed to fall freely from the opening.
However, with the developing apparatus like this, a censor for detecting the concentration of toner, a driving source for supplying toner when the toner concentration decreases, a device including a control circuit, and a mechanism for reciprocating the toner cartridge, are necessary to be provided, and the apparatus becomes inevitably complicated and expensive. Further, in the case of the apparatus counted with the mechanism for reciprocating the toner cartridge, vibration is transmitted to the image forming apparatus itself and there is a possibility of occurring image deterioration due to the influence of the vibration to other mechanisms of the machine.
To solve the problem mentioned above the applicant of the present invention proposed in Japanese Patent Laid-Open Publication No. 2001-235933, which relates to a developing apparatus of so-called one-component developing system in which only toner is carried on its developing roller a developing apparatus in which the driving force of toner transfer means in a toner container is obtained from a driving source for driving the developing roller, etc. of the developing apparatus and the toner is transferred by the transfer means and allowed to fall freely from a toner receiving opening formed in an end of the developing apparatus, thus the toner can be supplied without a particular driving source, control circuit, and reciprocating mechanism. Further, the applicant proposed a means to prevent the clogging of toner by reducing partially the transferring ability of an agitation/transfer means in the downstream zone from the position where toner falls on the agitation/transfer means, because when toner is transferred uniformly by the agitation/transfer means, the toner supplied from the toner receiving opening is transferred immediately and toner is further supplied from the toner receiving opening, resulting in excessive supply of the toner and the clogging of toner is induced.
However, with the developing apparatus proposed in said Japanese Patent Laid-Open Publication No. 2001-235933, when, for example, the maximum size of recording medium handled in the image forming apparatus is A4 or so, the toner can be supplied without the occurrence of toner clogging by determining the clearance between the periphery of the agitation/transfer means and inner wall of the developing apparatus to be 1mm or so. But, in the case of an image forming apparatus in which large recording medium such as A3 size is handled, there arises the necessity for increasing said clearance to 2 mm or so, because it is concerned that deflection increases in the agitation/transfer means; whereas if the clearance between the periphery of the agitation/transfer means and inner wall of the developing apparatus is increased like this, then the supplied toner is formed into a lump like soft cake in the clearance, that is, so-called soft caking occurs. Accordingly, the toner supplied from the toner container can not fall and toner supply to the agitation/transfer means is obstructed, resulting in problems such as the occurrence of irregular image formation, etc. due to toner shortage.
Further, when removing the toner container emptied out from the developing apparatus, the toner remained in the toner container may fall onto the agitation/transfer means of the developing apparatus. Then, the toner piles on the agitation/transfer means in the developing apparatus proper and forms into a lump like soft cake, which hinders free falling of the toner, and the supply of toner to the developing apparatus proper is obstructed and the amount of toner in the developing apparatus proper decreases, resulting in insufficient supply of toner to the developing roller. As a result, problems such as irregular image formation may occur.
As to the leveling off of the piled toner a developing apparatus is disclosed in Japanese Patent No. 3078501. In the developing apparatus, when filling toner from a cartridge to a toner hopper provided on the upper part of the developing apparatus, the toner fallen onto the toner hopper is leveled off by the mounting/demounting of the cartridge and the opening/closing action of a shutter. However, with the developing apparatus, the toner is leveled off when the toner hopper provided on the upper part thereof is emptied and all of the toner in the cartridge is transferred to the toner hopper; whereas with the developing apparatus disclosed in said Japanese Patent Laid-Open Publication No. 2001-235933, only the amount of toner corresponding to consumed amount of toner is allowed to fall freely onto the agitation/transfer means without using a particular driving source and control circuit, and by this the toner piled on the agitation/transfer means is not leveled off. With the developing apparatus of said Japanese Patent No. 3078501, a complicated mechanism is required for moving a leveling plate or leveling member together with the mounting/dismounting of the cartridge and the opening/closing action of the shutter, and the cost of the apparatus increases inevitably.
Therefore, in the developing apparatus of an image forming apparatus, in which the toner is allowed to fall onto the agitation/transfer means without the necessity of providing on the toner container side a driving source for supplying the toner and control circuit for controlling the driving source, there is a problem to be solved so that the occurrence of irregular image formation is prevented, which is caused by insufficient supply of toner to the developing roller due to the shortage of toner in the developing apparatus owing to the phenomenon that the toner is clogged in the clearance between the periphery of the agitation/transfer means and inner wall of the developing apparatus to be formed into a lump like soft cake and the free-falling thereof is hindered when a container containing new toner is mounted in the case the clearance is increased.
There is also a problem to be solved so that the occurrence of irregular image formation is prevented, which is caused by the phenomenon that when removing the toner container from the developing apparatus the toner remained in the toner container may fall onto the agitation/transfer means of the developing apparatus and piles thereon to be formed into a lump like soft cake, and then when a container containing new toner is mounted the toner is hindered from free falling and the supply of toner to the developing apparatus become impossible.